In the past, a vehicle-mounted radar apparatus derives a position of a target with respect to a vehicle (radar apparatus) by transmitting a transmission wave from a transmitter antenna and receiving a reflection wave from the target by a receiver antenna. The detailed process thereof is as follows. A signal processing unit of the radar apparatus generates a beat signal by mixing a transmitting signal corresponding to the transmission wave of which a frequency is changed in a given period, and a receiving signal corresponding to the reflection wave. That is, the signal processing unit generates the beat signal based on a frequency difference (beat frequency) between the transmitting signal and the receiving signal in each period including an up period in which the frequency ascends in a predetermined period, and a down period in which the frequency descends in a predetermined period.
Then, the signal processing unit generates a signal (transformed signal) for every frequency by processing the beat signal through FFT (Fast Fourier Transform). Among the transformed signals, a signal exceeding a threshold of a predetermined signal level is extracted as a peak signal. The signal processing unit derives paired data by pairing the peak signal of the up period and the peak signal of the down period based on a given condition.
For example, the signal processing unit derives paired data (predicted paired data) predicting the current paired data based on the paired data which is derived in the past, and derives a peak signal (predicted peak signal) predicting the current peak signal. And, the signal processing unit extracts a peak signal (predicted peak signal) predicting the current peak signal from the predicted paired data. And, the signal processing unit extracts the current peak signal included in a predetermined range, with a frequency of the predicted peak signal being as a base point, as a current peak signal corresponding to the predicted peak signal, for every up period and down period. The signal processing unit derives paired data by pairing the peak signal of each corresponding period from the frequency of the extracted peak signal and the angular information.
The signal processing unit derives a distance (vertical distance) from the vehicle to the target, or a distance (horizontal distance) of the target with respect to a vehicle running in a direction substantially perpendicular to a traveling direction of the vehicle. Further, the signal processing unit derives a relative speed of the target with respect to the vehicle. The signal processing unit outputs determined information about the target, including the position of the target and the relative speed of the target, to a vehicle control device, so that the vehicle control device performs necessary vehicle control according to the target information. In this instance, the technology associated with the present invention is disclosed in Patent Documents 1 and 2, for example.
Patent Document 1: Japanese Patent Application Publication No. 2010-002265A
Patent Document 2: Japanese Patent Application Publication No. 2004-226120A
However, even for the reflection wave received from one target, a plurality of peak signals having different frequencies may appear within the predetermined range depending upon a material of the target. In the case where the plurality of peak signals having different frequencies appear, the pairing is conventionally performed by extracting the peak signal of a frequency closest to the frequency of the predicted peak signal. If the pairing is performed by this method, for example, two peak signals appear in the up period and the down period, respectively. Normally, even though the peak signals of the low frequency should be paired, in a case where the frequency of the peak signal of the high frequency approximates to the frequency of the predicted peak signal in the up period, and the frequency of the peak signal of the low frequency approximates to the frequency of the predicted peak signal in the down period, the peak signal of the high frequency in the up period and the peak signal of the low frequency in the down period may be paired.
Specifically, the reflection wave from the preceding vehicle includes a reflection wave from a bottom surface of the preceding vehicle near its center portion, in addition to the reflection wave from a rear portion of the preceding vehicle. If the rear portion of the preceding vehicle is made of metal or the like, power of the peak signal is strong since an intensity of the reflection wave from the rear portion is sufficiently high. Also, since the reflection wave from the bottom surface is not detected, or power of the peak signal is sufficiently weak even though it is detected, the possibility that mis-pairing occurs is low. However, if the rear portion of the preceding vehicle is made of resin or the like, the power of the peak signal is not high since the intensity of the reflection wave from the rear portion is not strong, so that the power may be equal to the power of the peak signal of the reflection wave from the bottom surface. In this instance, two peak signals appear, and if a method of pairing the peak signals approximating to the frequency of the predicted peak signal is used, the signals may be paired by which the one employs the peak signal of the rear portion, and the other employs the peak signal of the bottom surface.
In this way, in consequence of the mis-pairing when the paired data is derived, a variation in relative speed or the like occurs, thereby performing the vehicle control in a wrong way.